Paper 4

Q1. In which one of the following situations a chemical reaction does not occur?

(a) Milk is left open at room temperature during summer  

(b) Grapes get fermented  

(c) An iron nail is left exposed to humid atmosphere  

(d) Melting of glaciers  

**Answer: (d) Melting of glaciers**  

**Solution:** Melting of glaciers is a physical change (change of state from solid to liquid). The others involve chemical reactions: (a) souring of milk (lactic acid formation), (b) fermentation (sugar to alcohol), (c) rusting of iron (oxidation).

#### Q2. In order to prepare dry hydrogen chloride gas in humid atmosphere the gas produced is passed through a guard tube (drying tube) which contains:

(a) Calcium chloride  

(b) Calcium oxide  

(c) Calcium hydroxide  

(d) Calcium carbonate  

**Answer: (a) Calcium chloride**  

**Solution:** Calcium chloride (CaCl₂) is a common drying agent used to absorb moisture from HCl gas. The others are not typically used for drying HCl in this context.

#### Q3. The property by virtue of which a solid material can be drawn into thin wires is called:

(a) malleability  

(b) ductility  

(c) rigidity  

(d) resistivity  

**Answer: (b) ductility**  

**Solution:** Ductility is the ability of metals (e.g., copper) to be drawn into wires without breaking. Malleability is for hammering into sheets, rigidity is stiffness, and resistivity is electrical resistance.

#### Q4. Select from the following a hydrocarbon having one C—C bond and one C≡C bond:

(a) Benzene  

(b) Cyclohexane  

(c) Butyne  

(d) Propyne  

**Answer: (d) Propyne**  

**Solution:** Propyne (C₃H₄, structure: CH₃-C≡CH) has one single C—C bond and one triple C≡C bond. Benzene and cyclohexane lack triple bonds; butyne (C₄H₆, e.g., 1-butyne: CH₃-CH₂-C≡CH) has two C—C bonds and one C≡C bond. (Note: The Hindi version mentions C=C, but based on options and context, it's likely a reference to triple bond in English.)

#### Q5. The essential element taken up from the soil by the plants to synthesize proteins is:

(a) Phosphorus  

(b) Nitrogen  

(c) Iron  

(d) Magnesium  

**Answer: (b) Nitrogen**  

**Solution:** Nitrogen is fixed from the soil (via nitrates) and used to form amino acids, which build proteins. Phosphorus is for ATP/DNA, iron for chlorophyll/enzymes, and magnesium for chlorophyll.

#### Q6. Select TRUE statements about lymph from the following:  

A. Lymph vessels carry lymph through the body and finally open into larger arteries.  

B. Lymph contains some amount of plasma, proteins and blood cells.  

C. Lymph contains some amount of plasma, proteins and red blood cells.  

D. Lymph vessels carry lymph through the body and finally open into larger veins.  

The true statements are:  

(a) A and B  

(b) B and D  

(c) A and C  

(d) C and D  

**Answer: (b) B and D**  

**Solution:** Lymph drains into veins (not arteries, so A and C are false). It contains plasma, proteins, and white blood cells (B is true; C specifies red blood cells, which are minimal in lymph).

#### Q7. Plants like rose and banana have lost the capacity to produce:

(a) flowers  

(b) buds  

(c) seeds  

(d) fruits  

**Answer: (c) seeds**  

**Solution:** Many varieties of rose and banana are seedless and reproduce vegetatively (e.g., via cuttings or suckers). They still produce flowers, buds, and fruits.

#### Q8. In a bisexual flower the male gametes are present in the:

(a) anther  

(b) ovary  

(c) stigma  

(d) filament  

**Answer: (a) anther**  

**Solution:** Male gametes (pollen grains containing sperm) are produced in the anther of the stamen. Ovary and stigma are female parts; filament supports the anther.

#### Q9. When a pure-tall pea plant is crossed with a pure-dwarf pea plant, the percentage of tall pea plants in F₁ and F₂ generation pea plants will be respectively:

(a) 100%; 25%  

(b) 100%; 50%  

(c) 100%; 75%  

(d) 100%; 100%  

**Answer: (c) 100%; 75%**  

**Solution:** In Mendel's monohybrid cross (TT × tt), F₁ is all tall (Tt, 100% tall due to dominance). F₂ (Tt × Tt) is 3:1 tall:dwarf (75% tall).

#### Q10. To get an image of magnification -1 on a screen using a lens of focal length 20 cm, the object distance must be:

(a) Less than 20 cm  

(b) 30 cm  

(c) 40 cm  

(d) 80 cm  

**Answer: (c) 40 cm**  

**Solution:** For a convex lens, magnification m = -1 (real, inverted, same size) implies |v| = |u|. Using lens formula: 1/f = 1/v - 1/u. With u = -40 cm (object distance), v = +40 cm, f = +20 cm: 1/20 = 1/40 - (-1/40) = 2/40 = 1/20 (satisfies).

#### Q11. An optical device 'X' is placed obliquely in the path of a narrow parallel beam of light. If the emergent beam gets displaced laterally, the device 'X' is:

(a) plane mirror  

(b) convex lens  

(c) glass slab  

(d) glass prism  

**Answer: (c) glass slab**  

**Solution:** A glass slab causes lateral displacement (shift) of a parallel beam without changing its direction. A mirror reflects, a lens converges/diverges, and a prism deviates and disperses.

#### Q12. A piece of wire of resistance 'R' is cut lengthwise into three identical parts. These parts are then connected in parallel. If the equivalent resistance of this combination is R', then the value of R/R' is:

(a) 1/9  

(b) 1/3  

(c) 3  

(d) 9  

**Answer: (d) 9**  

**Solution:** Cutting lengthwise into three identical parts means each has resistance R/3 (length halved? Wait, for equal parts along length, each is L/3, so R/3). In parallel: 1/R' = 3/(R/3) = 9/R → R' = R/9 → R/R' = 9.

#### Q13. An electric bulb is rated 220 V; 11W. The resistance of its filament when it glows with a power supply of 220 V is:

(a) 4400 Ω  

(b) 440 Ω  

(c) 400 Ω  

(d) 20 Ω  

**Answer: (a) 4400 Ω**  

**Solution:** Resistance R = V²/P = (220)² / 11 = 48400 / 11 = 4400 Ω.

#### Q14. The minimum number of identical bulbs of rating 4V; 6W, that can work safely with desired brightness, when connected in series with a 240 V mains supply is:

(a) 20  

(b) 40  

(c) 60  

(d) 80  

**Answer: (c) 60**  

**Solution:** Each bulb needs 4V for rated brightness. In series, total voltage = n × 4V = 240V → n = 240/4 = 60.

#### Q15. In the food chains given below. Select the most efficient food chain in terms of energy:

(a) Grass → Grasshopper → Frog → Snake  

(b) Plants → Deer → Lion  

(c) Plants → Man  

(d) Phytoplankton → Zooplankton → Small Fish → Big Fish  

**Answer: (c) Plants → Man**  

**Solution:** Energy efficiency decreases with more trophic levels (10% rule). The shortest chain (producer → primary consumer) transfers the most energy.

#### Q16. Which one of the following gets biomagnified at different levels in a food chain?

(a) Carbon monoxide  

(b) CFC's  

(c) DDT  

(d) Manure  

**Answer: (c) DDT**  

**Solution:** DDT (pesticide) accumulates and increases in concentration up the food chain (biomagnification). Others do not biomagnify in the same way.

#### Q17. Assertion (A): In large animals, oxygen can reach different parts of the animal's body easily.  

Reason (R): Respiratory pigments take up oxygen from the air and carry it to body tissues.

(a) Both A and R are true, and R is the correct explanation of A.  

(b) Both A and R are true, but R is not the correct explanation of A.  

(c) A is true, but R is false.  

(d) A is false, but R is true.  

**Answer: (d) A is false, but R is true.**  

**Solution:** A is false (large animals rely on circulation, not simple diffusion). R is true (e.g., hemoglobin transports oxygen).

#### Q18. Assertion (A): Concentrated nitric acid is diluted by adding water slowly to acid with constant stirring.  

Reason (R): Concentrated nitric acid is easily soluble in water.

(a) Both A and R are true, and R is the correct explanation of A.  

(b) Both A and R are true, but R is not the correct explanation of A.  

(c) A is true, but R is false.  

(d) A is false, but R is true.  

**Answer: (d) A is false, but R is true.**  

**Solution:** A is false (standard safety: add acid to water to avoid exothermic splashing). R is true (soluble), but not the reason for the method.

#### Q19. Assertion (A): In reptiles, the temperature at which the fertilized eggs are kept decides the sex of the offsprings.  

Reason (R): Sex is not genetically determined in some animals.

(a) Both A and R are true, and R is the correct explanation of A.  

(b) Both A and R are true, but R is not the correct explanation of A.  

(c) A is true, but R is false.  

(d) A is false, but R is true.  

**Answer: (a) Both A and R are true, and R is the correct explanation of A.**  

**Solution:** In some reptiles (e.g., turtles), sex is temperature-dependent (environmental), not genetic.

#### Q20. Assertion (A): When ciliary muscles contract, eye lens becomes thin.  

Reason (R): Ciliary muscles control the power of the eye lens.

(a) Both A and R are true, and R is the correct explanation of A.  

(b) Both A and R are true, but R is not the correct explanation of A.  

(c) A is true, but R is false.  

(d) A is false, but R is true.  

**Answer: (d) A is false, but R is true.**  

**Solution:** A is false (contraction makes lens thicker for near vision; relaxation makes it thin for distant). R is true (they adjust curvature/power).